Added a very simple checksum field to the init ramdisk.

This uncovers a bug where the bootloader may corrupt the initrd on x64.

This is probably related to our kernel64 hack..

mkinitrd/mkinitrd.cpp

@@ -49,6 +49,16 @@ bool writeall(int fd, const void* p, size_t size)
 	return true;
 }
 
+uint8_t ContinueChecksum(uint8_t checksum,  const void* p, size_t size)
+{
+	const uint8_t* buffer = (const uint8_t*) p;
+	while ( size-- )
+	{
+		checksum += *buffer++;
+	}
+	return checksum;
+}
+
 void usage(int argc, char* argv[])
 {
 	printf("usage: %s [OPTIONS] <files>\n", argv[0]);
@@ -136,11 +146,16 @@ int main(int argc, char* argv[])
 		return 1;
 	}
 
+	// Keep track of the file checksum.
+	Sortix::InitRD::Trailer trailer;
+	trailer.sum = 0;
+
 	// Write the initrd headers.
 	Sortix::InitRD::Header header;
 	memset(&header, 0, sizeof(header));
 	strcpy(header.magic, "sortix-initrd-1");
 	header.numfiles = numfiles;
+	trailer.sum = ContinueChecksum(trailer.sum, &header, sizeof(header));
 	if ( !writeall(fd, &header, sizeof(header)) )
 	{
 		error(0, errno, "write: %s", dest);
@@ -209,6 +224,7 @@ int main(int argc, char* argv[])
 			return 1;
 		}
 
+		trailer.sum = ContinueChecksum(trailer.sum, &fileheader, sizeof(fileheader));
 		if ( !writeall(fd, &fileheader, sizeof(fileheader)) )
 		{
 			error(0, errno, "write: %s", dest);
@@ -242,6 +258,7 @@ int main(int argc, char* argv[])
 				return 1;
 			}
 
+			trailer.sum = ContinueChecksum(trailer.sum, &buffer, bytesread);
 			if ( !writeall(fd, buffer, bytesread) )
 			{
 				error(0, errno, "write: %s", dest);
@@ -259,5 +276,13 @@ int main(int argc, char* argv[])
 		close(filefd);
 	}
 
+	if ( !writeall(fd, &trailer, sizeof(trailer)) )
+	{
+		error(0, errno, "write: %s", dest);
+		close(fd);
+		unlink(dest);
+		return 1;
+	}
+
 	return 0;
 }

sortix/initrd.cpp

@@ -93,6 +93,16 @@ namespace Sortix
 			return 0;
 		}
 
+		uint8_t ContinueChecksum(uint8_t checksum,  const void* p, size_t size)
+		{
+			const uint8_t* buffer = (const uint8_t*) p;
+			while ( size-- )
+			{
+				checksum += *buffer++;
+			}
+			return checksum;
+		}
+
 		void Init(byte* theinitrd, size_t size)
 		{
 			initrd = theinitrd;
@@ -104,6 +114,15 @@ namespace Sortix
 			if ( size < sizeneeded ) { PanicF("initrd.cpp: initrd is too small"); }
 			// TODO: We need to do more validation here!
 
+			Trailer* trailer = (Trailer*) (initrd + initrdsize - sizeof(Trailer));
+			uint8_t checksum = ContinueChecksum(0, initrd, initrdsize - sizeof(Trailer));
+			if ( trailer->sum != checksum )
+			{
+				PanicF("InitRD Checksum failed: the ramdisk may have been "
+				       "corrupted by the bootloader: Got %u instead of %u\n",
+				       checksum, trailer->sum);
+			}
+
 			Syscall::Register(SYSCALL_PRINT_PATH_FILES, (void*) SysPrintPathFiles);
 			Syscall::Register(SYSCALL_GET_FILEINFO, (void*) SysGetFileInfo);
 			Syscall::Register(SYSCALL_GET_NUM_FILES, (void*) SysGetNumFiles);

sortix/initrd.h

@@ -49,6 +49,11 @@ namespace Sortix
 			char name[128];
 		};
 
+		struct Trailer
+		{
+			uint8_t sum; // sum of all bytes but the trailer.
+		};
+
 #ifdef SORTIX_KERNEL
 		void Init(byte* initrd, size_t size);
 		byte* Open(const char* filepath, size_t* size);